Flux residue left after hand or wave soldering should be cleaned off with a PCB cleaner while the board is unpowered. Micron 3400 Protektor PCB Cleaner is a solvent-based PCB cleaner and degreaser whose page says it removes light flux residue, dissolves wave-soldered flux residues and misprinted solder paste, and evaporates to a clean, dry, residue-free surface. Clean before conformal coating so the coating does not lift.
Why it happens
- Flux residues not removed after soldering. Hand soldering and wave soldering both leave flux around joints.
- Misprinted solder paste. Paste wiped off a misprint can leave a film behind.
You will see sticky or white residue near joints. Under conformal coating, residue causes the coating to lift or bubble.
How to fix it
- Flux residue on PCB assemblies: Micron 3400 Protektor PCB Cleaner, as a 550 ml aerosol or 1 L bulk liquid. Its page describes it as a fast-drying flux remover and PCB degreaser, specifically formulated for delicate electronics, non-ionic and non-corrosive, with excellent cleaning efficiency at room temperature.
The 3400 page does not give step-by-step directions. Follow the instructions on the can and the TDS. Around the cleaning itself:
- Power off and disconnect the board.
- Work in a ventilated area away from ignition sources.
- Apply the cleaner as the can and TDS direct.
- Let the board dry completely before powering it or coating it.
- Inspect under magnification for residue left under components.
If you are cleaning before conformal coating, the 3400 page says it provides a clean surface for re-application of conformal coating.
What to avoid
- Boards must be unpowered. 3400 is a solvent: treat it as flammable until the SDS says otherwise, keep it away from sparks, flames and hot surfaces, and use ventilation.
- Test on sensitive plastics before use, such as connectors, displays and clear parts.
- Do not power the board or coat it until it is fully dry.
- Do not leave dissolved flux pooled under components; let it run off or wick it away.
When to ask an expert
Ask Micron technical if:
- you need ionic contamination testing or must meet a cleanliness specification;
- residue keeps coming back on a production line, which may mean the flux or soldering process needs review;
- you are cleaning high-reliability assemblies (defence, medical, automotive) with their own process rules.
FAQ
Why should I clean flux off at all?
Flux residue can be sticky, attract dust and moisture, and stop conformal coating from bonding. Cleaning it gives a clean surface for coating and inspection.
Can I clean flux off a board while it is running?
No. Power off and disconnect the board. 3400 is a solvent cleaner; treat it as flammable until the SDS confirms otherwise.
Does 3400 leave any residue?
Its page says it evaporates quickly, leaving a clean, dry, residue-free surface.
Is it safe on plastic components?
The page lists excellent material compatibility and says it is formulated for delicate electronics. Test on any sensitive plastic first.
Should I use the aerosol or the 1 L bulk?
The aerosol suits rework benches and spot cleaning. The 1 L bulk liquid suits production cleaning where boards are cleaned with a brush or in a tray. Both are the same cleaner; follow the TDS for either.
White residue came back after cleaning. Why?
Some residues spread rather than dissolve if too little cleaner is used or it dries on the board before carrying the residue off. Clean again, let the cleaner run off the board, and check that the flux type is one a solvent cleaner can remove. If it keeps returning, ask Micron technical about your flux.
See the product: Micron 3400 Protektor PCB Cleaner. More electronics fixes: electronics hub.